The present invention relates generally to imaging print media.
It is generally known that errors may occur as media is fed through an image forming apparatus during printing operations. The errors may occur in the scan and media feed directions and may affect dot placement upon the media. It is also generally known that the media may expand or contract with changes in the moisture content of the media. In one respect, media expansion may occur because print media is typically composed, at least in part, of cellulose or some other absorbent material which often expands as it absorbs water. Therefore, as ink is sprayed or fired onto the media, the media may absorb the ink and expand. One problem associated with feed errors and media expansion or contraction is that placement of subsequently applied ink drops may not reach their intended targets. This may result in poor print quality, as the ink drops may not be arranged on the media as intended.
In some printing processes, such as with laser printers, the media may be heated, which may result in evaporation of some moisture from the media, thus causing the media to contract. This may result in media movement within the printing apparatus. Such movement may ultimately result in printing errors, and improper advancement of the media through the printing apparatus. Again, print media movement may deteriorate the quality of the image produced, and in some cases, may render the image produced entirely unacceptable.
It is often possible to measure media feed as well as media expansion/contraction (e.g., dimensional change in the media) errors. One manner involves the use of relatively sophisticated cameras having relatively high degrees of accuracy. These cameras typically have limited fields of vision. For instance, the size of an object that may be captured within a single picture may be relatively limited. According to this manner, a pair of cameras is typically placed along a media feed direction at a predetermined distance from each other. However, when the media feed distance to be measured is small (e.g., on the order of xe2x85x9 of an inch or smaller), it is not possible to measure with sufficient accuracy, any feed errors between consecutive media feed operations due to the physical limitations of these types of cameras.
According to an embodiment, the invention pertains to a method of imaging material. In the method, a section of a medium is photographed with a first camera having a first field of view. The medium is advanced along a feed direction and the section is photographed with a second camera having a second field of view. At least one of the first field of view and the second field of view is shifted from a nominal location by one or more reflective surfaces. An actual advance of the medium is compared with an intended advance of the medium and it is determined whether at least one of a media advance error and a dimensional change in the media exists in response to the comparing step.
In another embodiment, the invention relates to a system for imaging print media configured to advance along a feed direction. The system includes a first camera assembly including a first camera having a first field of view and at least one reflecting surface configured to shift the first field of view from a nominal location and a second camera assembly having a second camera. The system also includes a computer configured to receive images photographed by the first camera and the second camera. The computer is also configured to determine a vector indicating a distance traveled by an section of the print media photographed by the first camera and the second camera.
In accordance with a further embodiment, the invention relates to an apparatus for determining errors during printing operations of a printing device having a media feed direction. The apparatus includes a first camera assembly having a camera with a first field of view and at least one reflective surface to deflect the first field of view from a nominal location. The apparatus also includes a second camera assembly having a camera with a second field of view. The first camera and the second camera are configured to photograph a section of media contained in the printing device. In addition, the second camera assembly is positioned at a location substantially downstream of the first camera assembly along the media feed direction of the printing device.
According to a yet further embodiment, the invention pertains to an apparatus for imaging print media. The apparatus includes first means for photographing a section of the print media having a first field of view. The apparatus also includes second means for photographing the section of the print media having a second field of view. In addition, the apparatus includes means for deflecting the first field of view from a nominal location toward the second field of view and means for determining whether at least one of a media advance error and a dimensional change in the media exists.
Features and aspects of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings, in which:
FIG. 1 shows a simplified front view of a device according to an embodiment of the invention;
FIG. 2 shows an enlarged cross-sectional side view along lines IIxe2x80x94II in FIG. 1;
FIGS. 3A-3B, collectively, illustrate a manner of implementing the device of FIG. 1 according to a first embodiment of the invention;
FIGS. 4A-4B, collectively, illustrate another manner of implementing the device of FIG. 1; and
FIG. 5 shows a cross-sectional side view similar to FIG. 2 according to another arrangement of the invention.